Mr Cameron has said he is hoping to finalise a deal on new membership terms in February, with the nation expected to go to the polls in June.

Asked if the PM should stand down if Britain votes to leave, Mr Cleverly told Pienaar's Politics on BBC Radio Five Live: "I don't see that that has to be the case at all.

"I think that the biggest thing for us, looking internally just for a moment, I think the biggest thing for the Conservative Party is that there will be Conservatives on both sides of the argument."

When questioned on whether ministers should be allowed to campaign for leaving the EU, Mr Cleverly said: "I think there's a big pragmatic argument for that for no other reason than the parliamentary maths.

"There are only 300 or so MPs from which the Prime Minister can draw a government and almost 100 seats in government to fill. I think that will be the pragmatic option.

Lord Baker Photo: IAN JONES

"But if we conduct the campaign in a friendly, professional, tough but gallant way, I don't see any reason why anyone at the head of either side of the argument will need to stand down irrespective of what the result will be."